METHOD FOR PRODUCING PRODUCTS BASED ON WOOD AS A RAW MATERIAL
20240076831 ยท 2024-03-07
Inventors
- Anton Friedl (Vienna, AT)
- Maximilian LEHR (Vienna, AT)
- Martin MILTNER (Maria Anzbach, AT)
- Walter WUKOVITS (Drassburg, AT)
Cpc classification
International classification
D21C9/08
TEXTILES; PAPER
Abstract
A method is disclosed for producing products based on wood as a raw material. The method includes wood, in the form of wood particles, being subjected to an extraction treatment using an extracting agent. The extracting agent may include one or more organic solvents in an organic-aqueous mixture of the solvent or solvents with water. A content of fatty acids in the wood particles is reduced, by the extraction treatment of the wood particles using the solvent, by at least 70%, measured as hexanal content in wt. % after accelerated aging for 72 h at 90 C., while the content of cellulose, hemicelluloses and lignin is largely maintained during this extraction treatment.
Claims
1. A method for producing products based on wood as a raw material comprising: wood in the form of wood particles being subjected to an extraction treatment with an extracting agent, wherein the extracting agent comprises one or more organic solvents in an organic-aqueous mixture of the solvent or solvents with water, wherein the content of fatty acids in the wood particles is reduced by at least 70%, measured as the hexanal content in wt % after accelerated aging for 72 h at 90 C., by the extraction treatment of the wood particles with the extracting agent, and wherein the content of cellulose, hemicelluloses and lignin is substantially maintained in the extraction treatment.
2. The method according to claim 1, wherein the wood particles are present in a size of at most 2 mm, wherein the particle size is preferably defined according to the National Renewable Energy Laboratory (NREL) Laboratory Analytical Procedure (LAP) NREL/TP-510-42620 Preparation of Samples for Compositional Analysis by the screen mesh of 2 mm of the cutting mill for sample preparation, and wherein the wood particles are preferably present in the form of fibers, chips or mixtures thereof.
3. The method according to claim 1, wherein the wood particles are wood frayed by mechanical and/or thermal and/or chemical digestion, in particular wood fibers with average fiber lengths between 0.5 and 2 mm and average fiber diameters between 10 and 50 m, and wherein the average fiber length as well as the average fiber diameter relate to the length average determined by optical measurement of the suspended fibers.
4. The method according to claim 1, wherein the solvent portion of the organic-aqueous mixture in the extracting agent, determined as the concentration of the liquid phase of the extract, is composed of 0-95 wt % of ethanol, preferably 50-90 wt % of ethanol, 0-99 wt % of acetone, preferably 30-90 wt % of acetone, 0-70 wt % of n-propanol, 0-85 wt % of iso-propanol and/or 0-99 wt % of methanol.
5. The method according to claim 1, wherein the content of cellulose, hemicelluloses and lignin is reduced by less than 10%, preferably by less than 5%, in particular by less than 4%, in the extraction treatment, wherein this reduction is preferably ascertained as an extracted solid mass related to the basic material, the wood particles.
6. The method according to claim 1, wherein the wood particles are selected from coniferous wood particles, preferably spruce wood particles, fir wood particles, pine wood particles or larch wood particles; deciduous wood particles, in particular beech wood particles, poplar wood particles, birch wood particles or eucalyptus wood particles; or mixtures thereof.
7. The method according to claim 1, wherein the wood particles are purified once or multiple times with an extracting agent after the treatment with the extracting agent, preferably purified with an organic-aqueous solvent with a similar or identical concentration as that of the extracting agent.
8. The method according to claim 1, wherein the content of fatty acids in the wood particles is reduced by at least 75%, preferably by at least 80%, in particular by at least 90%, measured as the hexanal content in wt % of the wood particles in the basic material compared to the extracted wood particles after accelerated aging for 72 h at 90 C., by extraction of the wood particles with the extracting agent.
9. The method according to claim 1, wherein the content of fatty acids in the wood particles is reduced to a content below 2 mg/kg dry matter, preferably below 1 mg/kg dry matter, in particular of below 0.5 mg/kg dry matter, measured as the hexanal content as the mass portion of the extracted wood particles after accelerated aging for 72 h at 90 C., by extraction of the wood particles with the extracting agent.
10. The method according to claim 1, wherein resin acids are also extracted with the extraction besides the fatty acids.
11. The method according to claim 10, wherein the fatty acids, resin acids and/or optionally further extractives extracted with the extracting agent are supplied to a further purification method, preferably by mechanical separating technique after the thermal separation of the organic solvent from the organic-aqueous extracting agent, wherein lipophilic extractives, in particular fatty acids and resin acids, are precipitated and separated, and a liquid phase enriched with hydrophilic extractives, in particular lignans, is obtained, wherein the hydrophilic extractives are preferably further concentrated by subsequent treatment with thermal separating technique, in particular by means of membrane separating methods and/or adsorption.
12. The method according to claim 11, wherein a preceding membrane filtration of the extracting agent is effected in the extractive enrichment.
13. The method according to claim 1, wherein chelating agents, in particular chelating agents selected from multivalent and polyfunctional carboxylic acids, aminomethylcarboxylic acids, aminomethylphosphonic acids and the compounds thereof, EDTA, DTPA EGTA, EDDS and the salts thereof, polyphenols, tannins, amino acids, peptides, proteins, polycarboxylates, phosphates, polyphosphates, phosphonic acids, polyphosphonates, phosphated, phosphonylated, sulfated and sulfonated polymers are not added to the wood particles in the course of the extraction method, in particular in the course of the entire production method for the products produced from the wood particles.
14. The method according to claim 1, wherein the extracting agent as well as optionally used washing liquids, in particular water, are regenerated for reuse.
15. The method according to claim 1, wherein in addition to the reduction of the hexanal content, the mechanical strength of the extracted wood particles, measured as the tensile index of sample sheets in Nm/g, is also increased by at least 10%, preferably by at least 15%, in particular by at least 25%, by the extraction treatment, wherein the degree of grinding, measured in SR, therein changes by less than 10%.
16. A use of the lipophilic extractive fraction obtained according to claim 12 as an animal feed supplement.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] Further features of the invention are apparent from the claims, the figures and the description of figures. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of figures and/or shown in the figures alone are usable not only in the respectively specified combination, but also in other combinations without departing from the scope of the invention. Thus, implementations are also to be considered as encompassed and disclosed by the invention, which are not explicitly shown in the figures and explained, but arise from and can be generated by separated feature combinations from the explained implementations. Implementations and feature combinations are also to be considered as disclosed, which thus do not comprise all of the features of an originally formulated independent claim. Moreover, implementations and feature combinations are to be considered as disclosed, in particular by the implementations set out above, which extend beyond or deviate from the feature combinations set out in the relations of the claims. In particular, the present invention is explained in more detail based on the following examples and the figures, of course without being restricted thereto.
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DETAILED DESCRIPTION
[0059] The goal of the developed method in this patent is a significant improvement of the organoleptic characteristics of the wood particles as well as of aged wood particles, which are produced according to this method. The undesired odor of themin particular occurring after aging of the wood particles (up to 6 months) and flavor of the food coming in contact therewith, especially comes about by aldehydes (particularly hexanal), which are formed by an autocatalytic oxidation of fatty acids naturally occurring in the wood. This autocatalytic oxidation is, as above mentioned, currently industrially prevented or greatly decelerated by the complexation of the metal ions present in the wood particles, which act as a catalyst, by means of addition of chelating agents like for example ethylenediaminetetraacetic acid (EDTA). The method of this patent achieves a significant improvement of the organoleptic characteristics of the wood particles without addition of chelating agents, but by removal of potential aldehyde sources, especially fatty acids.
[0060] Since fatty acids as an aldehyde source and in further consequence source of organoleptic impairments of the wood particles can be satisfactorily quantified by measurement technique only with great effort, the hexanal content of the wood particles after aging was used for assessing the extraction success of the experiments of this patent. It is to be noted at this point that 0.5 mg/kg TM of hexanal (related to dry wood) mark that empirically ascertained value, below which organoleptic impairments are empirically no longer sensorially perceivable. For hexanal contents of the wood particles >0.5 mg/kg TM, it applies: the higher the hexanal content, the higher the organoleptic impairment of the wood particles.
[0061] The determination of the hexanal content can be effected via headspace gas chromatography (HS-GC) in that ca. 0.2 g of air-dry wood particles (90-95 wt % TSG) are filled into a headspace vial. In these vials, the wood particles then have to be aged sealed at room temperature (ca. 20 C.) for six months to oxidize the fatty acids to hexanal. Since this takes very much time and therefore does not allow soon assessment of the extraction success, the accelerated aging according to DIN ISO 5630-2 was performed for the present experiments (unless explicitly otherwise indicated). The wood particles were sealed in HS-GC vials, aged for 72 h at 90 C. and subsequently the hexanal content was ascertained by means of HS-GC. Although this standard for accelerated aging was withdrawn, the performed extraction experiments in table 1 show that the method of the accelerated aging provides comparable values and the hexanal values with the accelerated aging are even higher on average, respectively, and thereby even offer safeties with respect to the extraction success.
TABLE-US-00001 TABLE 1 Hexanal content, Hexanal content, Analyzed wood accelerated aged for 72 h naturally aged for 6 M. particles at 90 C. in mg/kg TM at 20 C. in mg/kg TM Basic material 11.37 10.62 Extracted wood 2.14 1.41 particles 1 Extracted wood 2.17 1.52 particles 2 Extracted wood 2.80 1.74 particles 3 Extracted wood 3.32 2.57 particles 4 Extracted wood 3.64 2.75 particles 5 Extracted wood 1.34 2.72 particles 6 Extracted wood 2.35 1.69 particles 7 Extracted wood 2.86 2.83 particles 8
[0062] For the extraction success of all of the experiments according to the present invention, the hexanal content was used since it empirically represents the main influencing factor of the organoleptic impairment of wood particles. The extractive content by means of Soxhlet extraction according to the TAPPI standard T204 is too inaccurate hereto, as table 2 shows. At this point, it is to be noted that for the determination of the extractive content of the wood particles of all of the experiments of this patent, not the TAPPI standard T204, but the NREL method NREL/TP-510-42619 very similar to the T204 was applied and groundwood or 2 mm sized wood particles were employed as the basic material instead of wood dust.
TABLE-US-00002 TABLE 2 Ascertained extractive content Hexanal content of Hexanal content of of the extracted the basic material the extracted wood wood particles in in mg/kg TM particles in mg/kg TM wt % related to Solvent average STABW average STABW the basic material Ethanol 14.07 1.13 <0.20 3.4 Ethanol 14.07 1.13 <0.20 3.0 Acetone 14.07 1.13 0.32 0.02 3.0 Acetone 14.07 1.13 0.27 0.01 2.6
[0063] As is apparent in table 2, the Soxhlet extractions with ethanol significantly differ from those with acetone in the hexanal content, but not significantly in the extractive content. This means that two differently extracted wood particles can for example have different organoleptic characteristics despite of non-significantly different extractive content. The hexanal content of the wood particles after aging is thus a substantially stronger and more accurate indicator for the organoleptic impairment than the extractive content, and therefore was used for the extraction success according to the present invention. In addition, the hexanal content of the basic material and the reduction of the hexanal content resulting from it was indicated for all of the experiments, since the basic materials are snapshots and the hexanal content therefore can possibly very greatly fluctuate.
[0064] Nevertheless, the extracted extractive mass (ascertained as evaporation residue of the extract) is an important indicator for the solid mass loss of the extractions since it nearly includes the entire extractively removed solid massexcept for some few very volatile compounds. Thus, the evaporation residue of the extract together with the hexanal content of the extracted wood particles is an important measure of the assessment of the selectivity of the extractions.
Experiment: Comparison Solvent Based on Soxhlet Extractions
[0065] For the solvent preselection, groundwood samples were extracted with three different solvents. 3 g of air-dry groundwood were respectively extracted for 24 h by means of Soxhlet method according to the NREL procedure NREL/TP-510-42619. The results are represented in table 3.
TABLE-US-00003 TABLE 3 Hexanal Hexanal Ascertained content content extractive content of the of the of the extracted basic extracted wood particles in Solvent 1 Solvent 2 material in groundwood wt % related to (24 h) (24 h) mg/kg TM in mg/kg TM the basic material Cyclohexane 11.32 2.36 1.0 Ethanol Cyclohexane 11.32 <0.20 3.4 Ethanol 11.32 <0.20 3.1 Ethanol 14.07 <0.20 3.0 Acetone 14.07 0.32 3.0
[0066] In table 3, it is apparent that even with higher hexanal contents of the basic material, ethanol extracts best, followed by acetone. Cyclohexane extracts worst by far, which means that completely nonpolar solvents are unsuitable for the extraction of fatty acids. According to Reichardt and Welton (Reichardt and Welton, Solvents and Solvent Effects in Organic Chemistry 4 (2011), Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA, pp 550-552), the empirically determined polarity of cyclohexane is 0 (very nonpolar) compared to 0.355 of acetone and 0.654 of ethanol. Nevertheless, the extraction with cyclohexane also could reduce the hexanal content by 79%.
Experiment 1: Extraction of Dry Groundwood
[0067] Based on the extraction of air-dry groundwood (consisting of ca. 95% of spruce and 5% of pine) with ethanol (EtOH), the influence of the parameters of solvent concentration, temperature and extraction duration was examined. Thereto, ca. 2 g of air-dry groundwood were extracted in an ethanol-water mixture with a solid: extracting agent ratio of 1:10 w/w and ethanol concentrations of 50, 70 and 90 wt % at temperatures of 70, 90 and 110 C. respectively for 0.5, 1, 2, 4 and 8 h in small autoclaves. After the extraction, the groundwood was squeezed, washed with ethanol, again squeezed and once again washed with demineralized water before it was dried, aged and analyzed. In
[0068] The
[0069] In table 4, it is visible that despite of the high hexanal content reductions achieved in this experimental series, the extracted solid mass is max. 7 wt % (related to the basic material)but mostly considerably below. This means with an ascertained extractive content of the basic material of ca. 3 wt %, that neither hemicelluloses nor lignin are extracted to appreciable extent.
TABLE-US-00004 TABLE 4 Extracted solid mass in wt % (related to the basic material) Extraction duration in h 0.5 1.0 2.0 4.0 8.0 70 C. 50 wt % EtOH 4.3 4.6 4.4 4.0 3.6 70 wt % EtOH 4.9 5.1 4.8 5.6 4.2 90 wt % EtOH 4.5 5.5 5.7 5.3 6.1 90 C. 50 wt % EtOH 3.7 3.5 4.0 4.7 5.1 70 wt % EtOH 4.0 4.4 4.8 4.8 5.4 90 wt % EtOH 5.5 5.6 5.9 5.8 5.6 110 C. 50 wt % EtOH 4.7 4.1 5.3 6.2 6.3 70 wt % EtOH 5.2 6.6 5.7 5.8 7.2 90 wt % EtOH 5.8 5.7 6.8 6.5 6.4
Experiment 2: Extraction Of Wet Groundwood With Ethanol On Different Conditions
[0070] The extraction of wet groundwood represents real conditions much better than the extraction of dry groundwood, like experiment 1, in particular in the cardboard production. In addition, substantially more sample mass was taken for these experiments (factor 225) than for experiment 1, to obtain a more meaningful result. Ca. 450 g TM of mechanically dehydrated groundwood (ca. 25 wt % TSG; ca. 95% of spruce and 5% of pine) were extracted in an ethanol-water mixture with a solid: solvent ratio of 1:10 w/w and ethanol concentrations of 60 wt % at temperatures of 70 and 90 C. for 2 and 4 h in an autoclave. After the extraction, the groundwood was squeezed, washed with ethanol, again squeezed and one again washed with demineralized water before it was dried, aged and analyzed. Table 5 shows the results of these extractions.
TABLE-US-00005 TABLE 5 Hexanal content Reduction Hexanal content of of the extracted of the EtOH Extraction conditions the basic material wood material hexanal content concentration Temperature Duration in mg/kg TM in mg/kg TM related to the in wt % in C. in h Average STABW Average STABW basic material 60 70 2 11.37 0.18 3.06 1.18 73% 60 70 4 11.37 0.18 2.15 1.00 81% 60 90 2 11.37 0.18 2.60 0.88 77% 60 90 4 11.37 0.18 2.49 1.50 78%
[0071] The experiments show thatcompared to the extraction of lower and especially air-dry wood material massthe experiments with mechanically dehydrated wood material and more sample mass have higher hexanal contents in the extracted wood material. Nevertheless, over 73% reduction of the hexanal content was achieved at each setting.
Experiment 3: Extraction Of Wet Groundwood With Three Different Organic Solvents
[0072] Experiment 3 was performed to test three different technically relevant solvents under real extraction conditions. Ca. 450 g TM of mechanically dehydrated groundwood (ca. 25 wt % TSG; ca. 95% spruce and 5% pine) were extracted in a solvent-water mixture with a solid: extracting agent ratio of 1:10 w/w and a solvent concentration of 70 wt % at a temperature of 70 C. for 4 h in an autoclave. After the extraction, the groundwood was squeezed, washed with extracting agent, again squeezed and once again washed with demineralized water before it was dried, aged and analyzed. Table 6 shows the results of these extractions.
TABLE-US-00006 TABLE 6 Evaporation residue of Reduction Hexanal content Reduction the extract in wt % of the Hexanal content of of the extracted of the related to the basic abietinic the basic material wood material hexanal content material dry matter acid content in mg/kg TM in mg/kg TM related to the Basic Extracted related to the Solvent Average STABW Average STABW basic material material Groundwood basic material Ethanol 96 14.07 1.13 4.92 0.40 65% 3.6 2.3 41% vol % non- denatured Ethanol 96 14.07 1.13 2.77 0.04 80% 3.6 2.4 48% vol % incompletely denatured with butanone Acetone 14.07 1.13 3.43 0.04 76% 3.6 2.2 55%
[0073] As is visible in table 6, acetone extracts the unsaturated fatty acids, which are responsible for the hexanal formation, significantly better than non-denatured ethanol. However, the best extraction results could be achieved with ethanol, which was incompletely denatured with butanone. The hexanal content of 2.77 mg/kg TM achieved herein with 70 wt %, 70 C. and 4 h extraction time is still considerably above the 0.5 mg/kg TM limit, but corresponds to a reduction of 80%. In all extractions, the evaporation residue of the extract is only between 2.2 and 2.4 wt % related to the basic material dry matter, which means with an ascertained extractive portion of 3.6 wt % that the wood main constituents cellulose, hemicelluloses and lignin de facto were not attacked and the extractions were thus very selective. The abietinic acid content of the extractions of this experiment was reduced by 41-55% related to the basic material. Since abietinic acid was here selected as a lead substance for the content of resin acids, a reduction of the content by around 50% is an indication of the considerable reduction of resin by the method of this patent.
Experiment 4: Extraction Of Wet Groundwood With Acetone At Different Solid-Extracting Agent Ratios
[0074] The influence of different solidextracting agent ratios was examined in this experiment. Ca. 200-450 g TM (according to solid: extracting agent ratio) of mechanically dehydrated groundwood (ca. 25 wt % TSG; ca. 95% spruce and 5% pine) were extracted in an acetone-water mixture consisting of 70 wt % of acetone and 30 wt % of demineralized water with solid: extracting agent ratios of 1:10, 1:15 and 1:25 w/w at a temperature of 50 C. for 1, 2 and 4 h in an autoclave. After the extraction, the groundwood was squeezed, washed with extracting agent, again squeezed and once again washed with demineralized water before it was dried, aged and analyzed. The results of these extractions are listed in table 7.
TABLE-US-00007 TABLE 7 Evaporation residue of Reduction the extract of the Hexanal content Reduction in wt % abietinic Hexanal content of of the extracted of the related to acid content Solid:extracting Extraction the basic material wood material hexanal content the basic related to agent ratio duration in mg/kg TM in mg/kg TM related to the material the basic w/w in h Average STABW Average STABW basic material dry matter material 1:10 4 14.07 1.13 5.83 0.18 59% 2.0 31% 1:15 4 14.07 1.13 2.76 0.15 80% 2.5 54% 1:15 2 7.24 0.03 1.19 0.72 84% 38% 1:25 2 7.24 0.03 0.94 0.23 87% 52% 1:10 1 2.44 0.11 0.40 0.04 84% 2.2 1:10 2 2.44 0.11 0.40 0.05 84% 1.5 1:15 2 2.44 0.11 0.39 0.01 84% 2.5 1:25 2 2.44 0.11 0.33 0.01 86% 2.8
[0075] As table 7 shows, the hexanal content is reduced by over 80% in all extractions (with the exception of the solid: extracting agent ratio of 1:10 (w/w) with a basic materialhexanal content of 14.07 mg/kg TM). With extracting agentsolid ratios above 10:1 (w/w), the reduction of the hexanal content under identical extraction conditions is comparably high and always far above 70% despite of different basic materialhexanal contents. Therein, the evaporation residue of the extract is less than 3%, which is an evidence for the quantitative preservation of the lignocellulose constituents in this method with ascertained extractive contents of the basic material of 3.4-3.7 wt %. This experiment too has shown that the method of this patent can significantly reduce resin by the reduction of the abietinic acid content by 31-54% related to the basic material.
Experiment 5: Multi-Stage Extraction Of Wet Groundwood With Acetone
[0076] In this experiment, multi-stage extractions were performed, wherein for each stage (=each one stage) fresh unloaded extracting agent was used. The groundwood (ca. 400-450 g TM; ca. 25 wt % TSG) was squeezed after each extraction stage (to ca. 30 wt % TSG) and mixed with acetone and demineralized water (both preheated to 50 C. extraction temperature) such that the solid: extracting agent ratio is 1:10 and the acetone concentration in the extracting agent is 70 wt %. The extractions were performed in an autoclave. After the extraction, the groundwood was squeezed, washed with extracting agent, again squeezed and once again washed with demineralized water before it was dried, aged and analyzed. The results of these extractions are listed in table 8.
TABLE-US-00008 TABLE 8 Evaporation Reduction Extraction residue of of the stage Hexanal content Reduction the extract abietinic number or Hexanal content of of the extracted of the in wt % acid content extraction the basic material wood material hexanal content related to the related to duration in mg/kg TM in mg/kg TM related to the basic material the basic Wood type in h Average STABW Average STABW basic material dry matter material 95% of 1 2.44 0.11 0.40 0.04 84% 2.2 62% spruce 2 2.44 0.11 <0.20 >92% 2.7 78% 5% of pine 3 2.44 0.11 <0.20 >92% 2.9 90% 4 2.44 0.11 <0.20 >92% 3.0 99% 95% of 1 9.43 0.66 0.98 0.19 90% 2.6 55% spruce 2 9.43 0.66 0.54 0.20 94% 3.2 80% 5% of pine 3 9.43 0.66 0.47 0.06 95% 3.3 95% 4 9.43 0.66 0.50 0.05 95% 3.4 100% 95% of 1 6.73 1.71 0.30 0.07 96% 1.9 spruce 2 6.73 1.71 0.23 0.04 97% 2.2 5% of fir 3 6.73 1.71 0.24 0.05 96% 2.3
[0077] As table 8 shows, the hexanal content is reduced by over 80% in all extractions already after the first stage, however, is still considerably over 0.50 mg/kg TM in particular with a basic material with higher hexanal contents. After stage three, however, the hexanal content is below 0.50 mg/kg TM, partially even below the determination limit of 0.20 mg/kg TM, with all extracted groundwoods of this experiment. Therein, the evaporation residue of the extract is less than 3-5%, which is an evidence for the quantitative preservation of the lignocellulose constituents in this method with ascertained extractive contents of the basic material of 2.5-3.7 wt %. This experiment too has shown that the method of this patent can significantly reduce resin, in particular with increasing extraction stage number, by the reduction of the abietinic acid content by 55-100% related to the basic material.
Experiment 6: Multi-Stage Extraction of Wet Wood Particles of Different Particle Sizes with Acetone
[0078] The influence of the particle size was examined with different extraction parameters in this experiment. Ca. 650 g TM of woodchips (ca. 20 mm; ca. 55 wt % TSG; spruce), ca. 450 g TM of chopped woodchips (2 mm mesh of the cutting mill screen; ca. 60 wt % TSG; spruce) and ca. 400 g TM of mechanically dehydrated groundwood (ca. 25 wt % TSG; ca. 95% spruce and 5% fir) were extracted respectively in two stages (each one hour) at 50 C. as well as respectively in two stages (each 30 min) at 21 C. in an autoclave. The multi-stage extractions were performed analogously to experiment 5 by squeezing the wood particles after each extraction stage and mixing with fresh unloaded extracting agent. Therein, the extraction parameters were 50 C., extraction durations of each 1 h per extraction stage and acetone concentrations of 70 wt % in the extracting agent (extraction parameter 1) as well as 21 C., extraction durations of each 30 min per extraction stage and pure acetone as admixed extracting agent, which results in acetone concentrations of 70-99 wt % according to extraction stage and particle size (extraction parameter 2). The solid: extracting agent ratios were selected such that the wood particles were just covered with extracting agent (1:6 with woodchips and ground woodchips and 1:10 with groundwood). After the extraction, the wood particles were squeezed (and washed with extracting agent with extraction parameter 1) and again squeezed before they were dried, aged and analyzed. The results of these results are listed in table 9.
TABLE-US-00009 TABLE 9 Reduction Evaporation Reduction of of the residue of the extract hexanal the extract evaporation Hexanal content content in wt % residue related Hexanal content of of the extracted related related to to the extract Wood Extraction the basic material wood material to the the basic evaporation residue particle Extraction duration in mg/kg TM in mg/kg TM basic material of the basic material shape parameter in h Average STABW Average STABW material dry matter Soxhlet extraction Woodchips 1 1.0 21.36 3.55 1.0 51% 2.0 21.36 3.55 17.10 2.32 20% 1.5 73% 2 0.5 21.36 3.55 0.7 35% 1.0 21.36 3.55 15.55 2.36 27% 0.9 46% Chopped 1 1.0 21.36 3.55 1.52 0.26 93% 1.7 84% woodchips 2.0 21.36 3.55 1.07 0.18 95% 2.1 100% 2 0.5 21.36 3.55 5.16 0.78 76% 1.3 65% 1.0 21.36 3.55 1.70 0.47 92% 1.6 79% Groundwood 1 1.0 6.73 1.71 0.30 0.07 96% 1.9 75% 2.0 6.73 1.71 0.23 0.04 97% 2.2 88% 2 0.5 6.73 1.71 2.18 1.11 68% 1.8 70% 1.0 6.73 1.71 0.41 0.07 94% 2.1 83%
[0079] As table 9 shows, the hexanal content of woodchips can only be decreased by ca. 20-30% with the method according to the invention. Upon grinding the woodchips to 2 mm particle size, as the NREL method NREL/TP-510-42620 also presets, in contrast, the hexanal content can be decreased to ca. 1 mg/kg TM, which corresponds to a reduction of ca. 95% with the starting hexanal content of 21.36 mg/kg TM, with the method according to the invention. With even lower particle size, such as for instance in groundwood, the reduction of the hexanal content with ca. 97% is even higher. The two extraction parameters provide comparable hexanal contents with larger particle size, whereas with smaller particle size, in particular groundwood, the extraction parameters 1 (higher temperature and longer extraction time) provide significantly better results. In the reduction of the extract evaporation residue related to the extract evaporation residue of the basic material Soxhlet extraction, the extraction parameters provide better results with all particle sizes. In table 9, it is additionally apparent that the reduction of the extract evaporation residue related to the extract evaporation residue of the basic material Soxhlet extraction cannot be used as an indicator for the extraction success of the intended method since for example with woodchips, even with high reduction of 73%, the hexanal content was only decreased by ca. 20, whereas with groundwood with a reduction of the extract evaporation residue related to the extract evaporation residue of the basic material Soxhlet extraction by 75%, the hexanal content could be decreased by ca. 96%.
Experiment 7: Alteration of the Mechanical Characteristics by the Extractive Treatment of Groundwood According to the Present Invention
[0080] This experiment serves for examining the effects of the extractive treatment on the mechanical characteristics of the extracted wood particles. Thereto, ca. 300-450 g TM (according to solid: extracting agent ratio) of mechanically dehydrated groundwood (ca. 25 wt % TSG) were extracted in a solvent-water mixture with solid: extracting agent ratios of 1:10 and 1:15 w/w and a solvent concentration of 60 and 70 wt % at temperatures of 50 C., 70 C. and 90 C. As the solvent, ethanol 96 vol % non-denatured (EtOH pure), ethanol 96 vol % incompletely denatured with butanone (EtOH den.) and acetone were employed. After the extraction, the groundwood was squeezed, washed with extracting agent, again squeezed and once again washed with demineralized water before sample sheets were formed therefrom, based on which the mechanical characteristics were examined. The mass loss results from the evaporation residue of the extract and is related to the basic material dry matter. In table 10, the results are listed.
TABLE-US-00010 TABLE 10 Average increase of the mechanical characteristics Stiffness Tensile Degree of Average Extraction conditions index index grinding mass loss Extracting measured measured measured by the Solvent Conc. agent ratio Temp. Time in Nm.sup.7/kg.sup.3 in Nm/g in SR extraction EtOH 60 wt % 1:10 70 C. 2 h 3% 25% 3% 2% pure 90 C. 4 h EtOH 70 wt % 1:10 70 C. 2 h 3% 41% 0% 2% pure 4 h 8 h EtOH 70 wt % 1:10 50 C. 4 h 4% 27% 6% 2% pure 1:15 70 C. EtOH 90 C. denatured acetone Acetone 70 wt % 1:10 50 C. 4 4% 20% 2% 3% 1 h Acetone 70 wt % 1:10 50 C. 3 2% 22% 4% 2% 1 h
[0081] As is visible in table 10, the degree of grinding and thus the dehydration of the groundwood hardly alters by the extraction, which entails the advantage with regard to a possible further processing (for example to cardboard) that existing production plants do not have to be retrofitted or converted. The stiffness index also only little alters by the extraction, whereas the tensile index as a measure of the breaking strength reproducibly highly increases. Compared to this high increase between 20 and 41% on average, the mass loss by the evaporation residue of the extract is very low with around 2%. This means that the wood particles over-proportionally highly gain strength by the extraction with low mass loss, which is in particular of great importance for the lightweighting trend in the packaging sector.
Experiment 8: Purification of the Extracted Extractives
[0082] In this experiment, mechanically dehydrated groundwood (ca. 25 wt % TSG; ca. 95% spruce and 5% fir) was extracted with a solidextracting agent ratio of 1:10 w/w at 50 C. for 1 h in an autoclave, wherein the extracting agent was composed of 70 wt % of acetone and 30 wt % of demineralized water. After the extraction, the groundwood was squeezed (to ca. 30 wt %) and the extract thus obtained was processed as follows:
[0083] First, the acetone was separated by distillation in that the distillation flask was heated up to 108 C. and distilled under atmospheric pressure up to the equilibrium setting. The remaining residue was centrifugated with 7197 g for 10 min and the sediment was subsequently separated from the supernatant. The supernatant was weighed and the dry substance content thereof was ascertained by gently drying at room temperature, which substantially corresponds to the content of extracted extractives. The sediment was also weighed and dissolved in defined mass of pure acetone. Analogously to the supernatant, the dry substance content thereof was determined. The deposits already precipitated in the distillation were also dissolved in pure acetone. Thereof, the dry substance content was determined analogously to the sediment. From the extract, the supernatant, the sediment dissolved in acetone and the deposits dissolved in acetone, the content of free fatty acids (linolenic acid, linolic acid, oleic acid and stearic acid, each expressed in linolic acid equivalents), resin acids (isopimaric acid, palustric acid, dehydroabietinic acid and abietinic acid, each expressed in abietinic acid equivalents) and lignans (i solariciresinol, secoisolariciresinol, conidendrinic acid, hydroxymatairesinol and matairesinol, each expressed in hydroxymatairesinol equivalents) was ascertained by means of gas chromatography. The results of experiment 1 and experiment 2 (repetitions with ident parameters) are listed in tables 11 and 12.
TABLE-US-00011 TABLE 11 Extract Deposits Supernatant Sediment Experiment 1 Average STABW Average STABW Average STABW Average STABW Mass in g 439.8 2.1 75.4 1.0 TSG in wt % 0.2 0.0 5.0 0.3 52.0 Content of 3.2 0.2 3.0 0.4 0.2 0.0 5.0 0.2 free fatty acids in the dry matter in wt % Content of 10.2 0.9 10.1 1.3 0.6 0.0 17.6 0.2 resin acids in the dry matter in wt % Content of 13.1 1.0 0.6 0.3 36.1 1.3 0.0 0.0 lignans in the dry matter in wt %
TABLE-US-00012 TABLE 12 Extract Deposits Supernatant Sediment Experiment 2 Average STABW Average STABW Average STABW Average STABW Mass in g 433.7 1.3 77.3 1.3 TSG in wt % 0.2 0.0 7.8 0.3 40.3 Content of 3.2 0.2 3.0 0.4 0.3 0.0 4.3 0.6 free fatty acids in the dry matter in wt % Content of 10.2 0.9 9.6 1.0 0.8 0.1 13.9 2.2 resin acids in the dry matter in wt % Content of 13.1 1.0 0.2 0.2 34.9 2.2 0.0 0.0 lignans in the dry matter in wt %
[0084] As it is visible in tables 11 and 12, the predominant extractive mass arises as a centrifugated sediment. Despite of the reduction of the amount of liquid by ca. 80% (from extract to supernatant), by the selected separating methods, the dry substance content (which here substantially corresponds to the extractive mass) in the supernatant is only at a similarly low level as in the extract (<1 wt %). However, the portion of free fatty acids and resin acids could be decreased to a very low level in the supernatant, whereas the lignans were enriched. In contrast, in the sediment and the deposits, there are few to no lignans, but a high content of free fatty acids and resin acids. Although the extractives analyzed here (free fatty acids, resin acids and lignans) only represent a part of the extractives (and dry substance found here), thus, it is uniquely apparent that with the selected thermal and mechanical separating method (distillation and centrifugation), not only the liquid phase (extract and supernatant, respectively) can be most widely freed from fatty and resin acids, but also lipophilic extractives (e.g. fatty acids and resin acids) and hydrophilic extractives (e.g. lignans) can respectively be significantly concentrated and purified as byproducts.
[0085] Key: [0086] STABW=standard deviation [0087] TM=dry matter [0088] TSG=dry substance content
Preferred Embodiments
[0089] In view of the above description of the present invention, the following preferred embodiments of the invention are herein disclosed:
[0090] 1. A method for producing products based on wood as a raw material, characterized in that wood in the form of wood particles is subjected to an extraction treatment with an extracting agent, which includes one or more organic solvents in an organic-aqueous mixture of the solvent or solvents with water, wherein the content of fatty acids in the wood particles is reduced by at least 70%, measured as the hexanal content in wt % after accelerated aging for 72 h at 90 C., by the extraction treatment of the wood particles with the extracting agent, but the content of cellulose, hemicelluloses and lignin is substantially maintained in this extraction treatment.
[0091] 2. The method according to embodiment 1, characterized in that the wood particles are present in a size of at most 2 mm, wherein the particle size is preferably defined according to the National Renewable Energy Laboratory (NREL) Laboratory Analytical Procedure (LAP) NREL/TP-510-42620 Preparation of Samples for Compositional Analysis by the screen mesh of 2 mm of the cutting mill for sample preparation.
[0092] 3. The method according to embodiment 1 or 2, characterized in that the wood particles are present in the form of fibers, chips or mixtures thereof.
[0093] 4. The method according to any one or more of the embodiments 1 to 3, characterized in that the wood particles are wood frayed by mechanical and/or thermal and/or chemical digestion.
[0094] 5. The method according to any one or more of the embodiments 1 to 4, characterized in that the wood particles are wood fibers with average fiber lengths between 0.5 and 2 mm and average fiber diameters between 10 and 50 m, wherein the average fiber length as well as the average fiber diameter relate to the length average determined by means of optical measurement of the suspended fibers.
[0095] 6. The method according to any one or more of the embodiments 1 to 5, characterized in that the solvent portion of the organic-aqueous solvent mixture in the extracting agent, determined as the concentration of the liquid phase of the extract, is composed of 0-95 wt % of ethanol, preferably 50-90 wt % of ethanol, 0-99 wt % of acetone, preferably 30-90 wt % of acetone, 0-70 wt % of n-propanol, 0-85 wt % of iso-propanol and/or 0-99 wt % of methanol.
[0096] 7. The method according to any one or more of the embodiments 1 to 6, characterized in that the ratio of extracting agent to solid dry substance is 5:1-25:1 (w/w), preferably 8:1-17:1 (w/w).
[0097] 8. The method according to any one or more of the embodiments 1 to 7, characterized in that the extraction treatment is effected at an extraction temperature of 20-150 C., preferably 40-120 C., in particular 50-110 C.
[0098] 9. The method according to any one or more of the embodiments 1 to 8, characterized in that the extraction treatment is effected at an absolute extraction pressure of 1-5 bar, preferably 1-1.49 bar.
[0099] 10. The method according to any one or more of the embodiments 1 to 9, characterized in that the extraction treatment is effected during an extraction time of 10 min-8 h, preferably 30 min-7 h, in particular 1-5 h.
[0100] 11. The method according to any one or more of the embodiments 1 to 10, characterized in that the method is used for producing cardboard, paper, wood fiber boards, chipboards, objects of utility, medical products, in particular for producing cardboard.
[0101] 12. The method according to any one or more of the embodiments 1 to 11, characterized in that the extraction treatment is selected from: [0102] treatment with ethanol at a concentration of at least 65 wt % at least at 65 C. for a period of time of at least 3 h; [0103] treatment with ethanol at a concentration of at least 65 wt % at least at 85 C. for a period of time of at least 30 min; [0104] treatment with ethanol at a concentration of at least 70 wt % at least at 105 C. for a period of time of at least 30 min; [0105] treatment with ethanol at a concentration of at least 45 wt % at least at 105 C. for a period of time of at least 5 h; [0106] treatment with acetone at a concentration of at least 50 wt % at least at 40 C. for a period of time of at least 30 min; or [0107] treatment with acetone at a concentration of at least 50 wt % at least at 20 C. for a period of time of at least 15 min.
[0108] 13. The method according to any one or more of the embodiments 1 to 12, characterized in that the treatment with the extracting agent is performed as a batch, continuous or semi-continuous extraction, preferably with a partial dwell time of at most 1 h per extraction step.
[0109] 14. The method according to any one or more of the embodiments 1 to 13, characterized in that the content of cellulose, hemicelluloses and lignin is reduced by less than 10%, preferably by less than 5%, in particular by less than 4%, in the extraction treatment, wherein this reduction is preferably ascertained as an extracted solid mass related to the basic material, the wood particles.
[0110] 15. The method according to any one or more of the embodiments 1 to 14, characterized in that the wood particles are selected from coniferous wood particles, preferably spruce wood particles, fir wood particles, pine wood particles or larch wood particles; deciduous wood particles, in particular beech wood particles, poplar wood particles, birch wood particles or eucalyptus wood particles; or mixtures thereof.
[0111] 16. The method according to any one or more of the embodiments 1 to 15, characterized in that the wood particles are mixed during the treatment with the extracting agent.
[0112] 17. The method according to any one or more of the embodiments 1 to 16, characterized in that the wood particles are squeezed after the treatment with the extracting agent to remove the extracting agent.
[0113] 18. The method according to any one or more of the embodiments 1 to 17, characterized in that the wood particles are purified once or multiple times with an extracting agent after the treatment with the extracting agent, preferably purified with an organic-aqueous solvent with a similar or identical concentration as that of the extracting agent.
[0114] 19. The method according to any one or more of the embodiments 1 to 18, characterized in that the extracting agent is removed from the wood particles by one-time or multi-time washing with water and/or water steam stripping and/or drying, preferably by water steam stripping and/or drying.
[0115] 20. The method according to any one or more of the embodiments 1 to 19, characterized in that the content of fatty acids in the wood particles is reduced by at least 75%, preferably by at least 80%, in particular by at least 90%, measured as the hexanal content in wt % of the wood particles in the basic material compared to the extracted wood particles after accelerated aging for 72 h at 90 C., by extraction of the wood particles with the extracting agent.
[0116] 21. The method according to any one or more of the embodiments 1 to 20, characterized in that the content of fatty acids in the wood particles is reduced to a content below 2 mg/kg dry matter, preferably below 1 mg/kg dry matter, in particular of below 0.5 mg/kg dry matter, measured as the hexanal content as the mass portion of the extracted wood particles after accelerated aging for 72 h at 90 C., by extraction of the wood particles with the extracting agent.
[0117] 22. The method according to any one or more of the embodiments 1 to 21, characterized in that resin acids are also extracted with the extraction besides the fatty acids.
[0118] 23. The method according to any one or more of the embodiments 1 to 22, characterized in that the fatty acids, resin acids and/or optionally further extractives extracted with the extracting agent are supplied to a further purification method, preferably by mechanical separating technique after the thermal separation of the organic solvent from the organic-aqueous extracting agent, wherein lipophilic extractives, in particular fatty acids and resin acids, are precipitated and separated, and a liquid phase enriched with hydrophilic extractives, in particular lignans, is obtained, wherein the hydrophilic extractives are preferably further concentrated by subsequent treatment with thermal separating technique, in particular by means of membrane separating methods and/or adsorption.
[0119] 24. The method according to embodiment 23, characterized in that a preceding membrane filtration of the extracting agent is effected in the extractive enrichment.
[0120] 25. The method according to any one or more of the embodiments 1 to 24, characterized in that chelating agents, in particular chelating agents selected from multivalent and polyfunctional carboxylic acids, aminomethylcarboxylic acids, aminomethylphosphonic acids and the compounds thereof, EDTA, DTPA EGTA, EDDS and the salts thereof, polyphenols, tannins, amino acids, peptides, proteins, polycarboxylates, phosphates, polyphosphates, phosphonic acids, polyphosphonates, phosphated, phosphonylated, sulfated and sulfonated polymers are not added to the wood particles in the course of the extraction method, in particular in the course of the entire production method for the products produced from the wood particles.
[0121] 26. The method according to any one or more of the embodiments 1 to 25, characterized in that the extracting agent as well as optionally used washing liquids, in particular water, are regenerated for reuse.
[0122] 27. The method according to any one or more of the embodiments 1 to 26, characterized in that in addition to the reduction of the hexanal content, the mechanical strength of the extracted wood particles, measured as the tensile index of sample sheets in Nm/g, is also increased by at least 10%, preferably by at least 15%, in particular by at least 25%, by the extraction treatment, wherein the degree of grinding, measured in SR, therein changes by less than 10%.
[0123] 28. The method according to any one or more of the embodiments 1 to 27, characterized in that at least 10% of water, preferably at least 7.5% of water, in particular at least 5% of water, are contained in the organic-aqueous mixture of the solvent or solvents.
[0124] Further preferred embodiments of the present invention are the following embodiments:
[0125] 1. A method for producing products based on wood as a raw material, characterized in that wood in the form of wood particles is subjected to an extraction treatment with an extracting agent, which includes one or more organic solvents or an organic-aqueous mixture of the solvent or solvents with water, wherein the content of fatty acids in the wood particles is reduced by at least 70%, measured as the hexanal content in wt % after accelerated aging for 72 h at 90 C., by the extraction treatment of the wood particles with the extracting agent, but the content of cellulose, hemicelluloses and lignin is substantially maintained in this extraction treatment.
[0126] 2. The method according to embodiment 1, characterized in that the wood particles are present in a size below 5 cm, wherein the particle size is preferably ascertained by sieving by means of square mesh screen, in particular by means of square mesh screen with a mesh of 5 cm or less.
[0127] 3. The method according to embodiment 1 or 2, characterized in that the wood particles are present in the form of fibers, chips, strands, woodchips or mixtures thereof.
[0128] 4. The method according to any one or more of the embodiments 1 to 3, characterized in that the wood particles are wood frayed by mechanical and/or thermal and/or chemical digestion.
[0129] 5. The method according to any one or more of the embodiments 1 to 4, characterized in that the wood particles are wood fibers with average fiber lengths between 0.5 and 2 mm and average fiber diameters between 10 and 50 m, wherein the average fiber length as well as the average fiber diameter relate to the length average determined by means of optical measurement of the suspended fibers.
[0130] 6. The method according to any one or more of the embodiments 1 to 5, characterized in that the solvent portion of the organic-aqueous solvent mixture in the extracting agent, determined as the concentration of the liquid phase of the extract, is composed of 0-95 wt % of ethanol, preferably 50-90 wt % of ethanol, 0-99 wt % of acetone, preferably 30-90 wt % of acetone, 0-70 wt % of n-propanol, 0-85 wt % of iso-propanol and/or 0-99 wt % of methanol.
[0131] 7. The method according to any one or more of the embodiments 1 to 6, characterized in that the ratio of extracting agent to solid dry substance is 5:1-25:1 (w/w), preferably 8:1-17:1 (w/w).
[0132] 8. The method according to any one or more of the embodiments 1 to 7, characterized in that the extraction treatment is effected at an extraction temperature of 20-150 C., preferably 40-120 C., in particular 50-110 C.
[0133] 9. The method according to any one or more of the embodiments 1 to 8, characterized in that the extraction treatment is effected at an absolute extraction pressure of 1-5 bar, preferably 1-1.49 bar.
[0134] 10. The method according to any one or more of the embodiments 1 to 9, characterized in that the extraction treatment is effected during an extraction time of 10 min-8 h, preferably 30 min-7 h, in particular 1-5 h.
[0135] 11. The method according to any one or more of the embodiments 1 to 10, characterized in that the method is used for producing cardboard, paper, wood fiber boards, chipboards, objects of utility, medical products, in particular for producing cardboard.
[0136] 12. The method according to any one or more of the embodiments 1 to 11, characterized in that the extraction treatment is selected from: [0137] treatment with ethanol at a concentration of at least 65 wt % at least at 65 C. for a period of time of at least 3 h; [0138] treatment with ethanol at a concentration of at least 65 wt % at least at 85 C. for a period of time of at least 30 min; [0139] treatment with ethanol at a concentration of at least 70 wt % at least at 105 C. for a period of time of at least 30 min; or [0140] treatment with ethanol at a concentration of at least 45 wt % at least at 105 C. for a period of time of at least 5 h; [0141] treatment with acetone at a concentration of at least 50 wt % at least at 40 C. for a period of time of at least 30 min.
[0142] 13. The method according to any one or more of the embodiments 1 to 12, characterized in that the treatment with the extracting agent is performed as a batch, continuous or semi-continuous extraction, preferably with a partial dwell time of at most 1 h per extraction step.
[0143] 14. The method according to any one or more of the embodiments 1 to 13, characterized in that the content of cellulose, hemicelluloses and lignin is reduced by less than 10%, preferably by less than 5%, in particular by less than 4%, in the extraction treatment, wherein this reduction is preferably ascertained as an extracted solid mass related to the basic material, the wood particles.
[0144] 15. The method according to any one or more of the embodiments 1 to 14, characterized in that the wood particles are selected from coniferous wood particles, preferably spruce wood particles, fir wood particles, pine wood particles or larch wood particles; deciduous wood particles, in particular beech wood particles, poplar wood particles, birch wood particles or eucalyptus wood particles; or mixtures thereof.
[0145] 16. The method according to any one or more of the embodiments 1 to 15, characterized in that the wood particles are mixed during the treatment with the extracting agent.
[0146] 17. The method according to any one or more of the embodiments 1 to 16, characterized in that the wood particles are squeezed after the treatment with the extracting agent to remove the extracting agent.
[0147] 18. The method according to any one or more of the embodiments 1 to 17, characterized in that the wood particles are purified once or multiple times with an extracting agent after the treatment with the extracting agent, preferably purified with an organic-aqueous solvent with a similar or identical concentration as that of the extracting agent.
[0148] 19. The method according to any one or more of the embodiments 1 to 18, characterized in that the extracting agent is removed from the wood particles by one-time or multi-time washing with water or drying, preferably by drying.
[0149] 20. The method according to any one or more of the embodiments 1 to 19, characterized in that the content of fatty acids in the wood particles is reduced by at least 75%, preferably by at least 80%, in particular by at least 90%, measured as the hexanal content in wt % of the wood particles in the basic material compared to the extracted wood particles after accelerated aging for 72 h at 90 C., by extraction of the wood particles with the extracting agent.
[0150] 21. The method according to any one or more of the embodiments 1 to 20, characterized in that the content of fatty acids in the wood particles is reduced to a content below 2 mg/kg dry matter, preferably below 1 mg/kg dry matter, in particular of below 0.5 mg/kg dry matter, measured as the hexanal content as the mass portion of the extracted wood particles after accelerated aging for 72 h at 90 C., by extraction of the wood particles with the extracting agent.
[0151] 22. The method according to any one or more of the embodiments 1 to 21, characterized in that resin acids are also extracted with the extraction besides the fatty acids.
[0152] 23. The method according to any one or more of the embodiments 1 to 22, characterized in that the fatty acids, resin acids and/or optionally further extractives extracted with the extracting agent are supplied to a further purification method.
[0153] 24. The method according to any one or more of the embodiments 1 to 23, characterized in that chelating agents, in particular chelating agents selected from multivalent and polyfunctional carboxylic acids, aminomethylcarboxylic acids, aminomethylphosphonic acids and the compounds thereof, EDTA, DTPA EGTA, EDDS and the salts thereof, polyphenols, tannins, amino acids, peptides, proteins, polycarboxylates, phosphates, polyphosphates, phosphonic acids, polyphosphonates, phosphated, phosphonylated, sulfated and sulfonated polymers are not added to the wood particles in the course of the extraction method, in particular in the course of the entire production method for the products produced from the wood particles.
[0154] 25. The method according to any one or more of the embodiments 1 to 24, characterized in that the extracting agent as well as optionally used washing liquids, in particular water, are regenerated for reuse.
[0155] 26. The method according to any one or more of the embodiments 1 to 25, characterized in that in addition to the reduction of the hexanal content, the mechanical strength of the extracted wood particles, measured as the tensile index of sample sheets in Nm/g, is also increased by at least 10%, preferably by at least 15%, in particular by at least 25%, by the extraction treatment, wherein the degree of grinding, measured in SR, therein changes by less than 10%.